The instant invention offers a simple very high speed valve system for controlling the ride qualities of air cushion vehicles. In particular, it is applicable to air cushion marine vehicles such as my Air Ride boat inventions. The air cushion vehicle is supported mostly by a pressurized air cushion located in its underside where the air cushion is supplied with pressurized gas from a gas pressurization device such as a powered blower. Latest Air Ride inventions are best represented by U.S. Pat. Nos. 4,739,719 and 5,000,107.
Practical applications of the Air Cushion Vehicle (ACV) technology such as Air Ride brought out the need for means to reduce pressure pulses that occur in the ACV's pressurized supporting air or gas cushion. Since the pressurized supporting gas cushion is essentially a large gas spring that generally supports some 85 percent or more of vehicle weight it is easy to see that sharp pressure pulses in the gas cushion can result in a rather harsh and bumpy ride in the vehicle.
The pressure pulses originate from water surface waves that pass into the gas cushion when the ACV is underway. The ACV generally has a flexible bow seal which allows the waves to enter the gas cushion relatively unmolested. Even very small surface waves can contribute to the problem with the pressure pulses rising over time in some instances. One reason for this is that the gas pressurization system, generally a powered blower, responds to small changes in cushion pressure and by so doing actually aggravates the situation. To understand how this works, consider that the blower moves toward a higher pressure when the pressure peak is rising and then goes toward a lower pressure when the pressure peak is falling. This is all well and good in theory; however, the blower response is lagging the pressure pulse rise and fall in pressure so the blower is actually contributing to the magnitude of the pressure pulses that the hull is feeling.
One approach to improve things is to utilize large diameter blowers that have flatter pressure vs. flow curves and lower rotational speeds. This helps in two ways: first, the flatter curve dictates that the blower will respond less to changes in pressure and second, the larger diameter blower wheel with its lower rotational speed means that the blower will take longer to change rotational speeds in response to pressure pulses.
When it is realized that typical pressure pulses occur at the rate of 2-3 cycles per second and that they are sharp and spike like in characteristic it is easy to understand the need to very carefully select the proper blower for an ACV. The total life of a typical pressure spike in an ACV can be on the order of 100 to 200 milliseconds. The maximum overpressure that occurs during that time varies but a pressure of 150 percent of normal or steady state gas cushion pressure is not uncommon. So, proper selection and design of the blower is essential to reduce the effects of pressure pulses on ACV ride qualities. However, even best selection of the blower still leaves a considerable amount of ride bounce due to the water surface generated gas cushion pressure pulses and the best blower still responds to pressure pulses but just to a lesser extent than a poorly selected blower.
The U.S. Navy has funded work to resolve the bouncy ride problem in their ACV's with particular emphasis on their Surface Effect Ships (SES) variants which are more complicated but similar in concept to my Air Ride boat inventions. The resulting solution is in the form of a Ride Control System (RCS) that is commercially manufactured in the United States. This RCS senses air cushion pressures and other hull operating characteristics and feeds such information into a microprocessor controller. The controller processes the input data and then outputs operating conditions to gas cushion vent valves and/or blower inlet flow control valves.
The gas cushion vent valves are operated in such manner so as to open and thereby vent pressure peaks as they occur in the supporting gas cushion. The blower inlet flow control valves accomplish essentially the same thing; however, they do so by restricting blower flow and pressure outputs in time with the pressure peaks. The commercially available RCS utilizes valves that are made up of a series of Venetian blind type overlapping louvers that are set in a rectangular frame. The louvers can be closed to essentially shut off gas flow or operated at various degrees of openness at frequencies that coincide with the pressure pulsing frequency in the supporting gas cushion.
This commercially available RCS utilizes a powered hydraulic cylinder to operate several vanes that are interconnected by mechanical linkages. Due to its inherent design characteristics, the two to six cycle per second hydraulically powered system in all probability requires high maintenance. It is easy to realize the difficult requirements put on this design when one considers that a typical SES ferry will see about forty million actuations of a single RCS vane per year. It has been reported that a RCS is now also manufactured in Sweden.
My instant invention utilizes special concepts in the vanes themselves to insure light weight construction and low moments of inertia. The low moment of inertia vane concept is combined with a way to create turbulence in the gas flow over the vane thus yielding balanced gas loading forces on the vane when operating. The two just discussed concepts that lower vane rotational force requirements are instrumental in allowing the present invention, in its preferred embodiment, to incorporate brushless electric servo motors each driving an individual vane. This approach eliminates hydraulic sealing problems and linkage wear and insures maximum vane drive system life. Further improvements include a fail safe vane braking and locking system that comes into play in the event of power failure and a venturi in the blower discharge to act as a check valve for the pressurized supporting gas cushion pressure peaks and thereby reduce the ability of the pressure peaks to reach the blower. Therefore, this venturi dramatically reduces the effects of gas cushion pressure peaks on blower operation. The features and improvements offered by the instant invention are discussed in the following sections.